Polyacetal resin (also referred to as polyoxymethylene resin, and abbreviated as POM resin) has well balanced mechanical qualities, and is excellent in abrasion resistance⋅abrasion characteristics, chemical resistance, thermal resistance, electrical characteristics, and the like, and is therefore widely utilized in the fields of automobiles, electric⋅electronic articles, and the like.
However, the demanded characteristics in these fields are gradually becoming more sophisticated, and as one example thereof, there is a strong demand for improving the basic sliding characteristics represented by the coefficient of friction and abrasion amount, along with in particular, suppressing the generation of creaking sounds when sliding, while maintaining the excellent surface smoothness of the polyacetal resin.
In order to respond to such requirements, methods of adding fluororesins or polyolefin resins to a polyacetal resin are known. However, fluororesins and polyolefin resins have poor compatibility with polyacetal resins. Therefore, these resins may separate from the polyacetal resin and cause detachment at the surface of a molded article, or generate deposits at a die when molding a molded article.
Further, a method of adding lubricating oils such as fatty acids, fatty acid esters, silicone oils, various mineral oils, and the like to a polyacetal resin is known. However, when molding a molded article, the polyacetal resin and the lubricating oil and the like may separate, whereby oozing out of the lubricating oil and the like may readily occur, and the oozed lubricating oil and the like may impair the extrusion processing properties and the molding processing properties. Further, if the lubricating oil and the like oozes out to the surface of the molded article, this may impair the appearance of the molded article.
In order to solve these problems, a polyacetal resin composition has been proposed wherein 0.5 to 40 parts by weight of a graft copolymer (B) wherein an olefin-based polymer (a) and one or two or more of a vinyl-based polymer or an ether-based polymer (b) are chemically bonded with a branched or crosslinked structure; 0.1 to 20 parts by weight of a lubricant (C); and 0.5 to 30 parts by weight of an inorganic powder (D) having an average particle diameter of 50 μm or less and further having a ratio of particles with a diameter of 100 μm or less of 95% or more; are added to and blended with 100 parts by weight of a polyacetal resin (A) (for example, refer to Patent Document 1).
Further, the selective combined use and blending of a hindered phenolic antioxidant; a specified nitrogenous compound; a specified graft copolymer; and a fatty acid ester; with a specified polyacetal resin has been proposed (for example, refer to Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. H03-111446
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2013-112727